Le, Tuan, and Chau Pham. “Evaluation Approaches of Sludge Ultrasonic Pretreatment Efficiency: A Review”. VNUHCM Journal of Science and Technology Development 16, no. 1 (March 31, 2013): 68-83. Accessed September 24, 2025. http://stdj.scienceandtechnology.com.vn/index.php/stdj/article/view/1389.